1. Field of the Invention
The present invention generally relates to testing of railroad telemetry radios used in intra-train communications and, more particularly, to a radio interference detection and screening system for Locomotive Control Unit (LCU) radios.
2. Background Description
Locomotive Control Unit (LCU) radios (also known generally as a railroad telemetry radio) and End of Train (EOT) radios are complementary devices which communicate with each other as part of a complete information and control system to be used on freight trains as required by the Federal Railway Administration (FRA). The EOT is typically mounted on the last car of the train and monitors train information such as, for example, brake pipe air pressure, train movement, battery condition, etc., and transmits this information to the LCU. The information monitored by the EOT and transmitted via a radio frequency (RF) link to the LCU and is displayed to the crew in the locomotive.
Since the proper operation of the LCU in intra-train communications is critical, the LCU system is tested on a regular basis and preferably before each use. Thus, after a train has been xe2x80x9cmade-upxe2x80x9d in the rail yard and the LCU and EOT installed, a functional test is performed to verify the overall operation of the LCU. This is done as part of the normal linking and arming sequence and verifies the functional operability of the LCU. This test does not check the performance limits of the LCU radios. To check radio performance, the LCU must normally be brought to a radio shop where the proper equipment is available, and requires opening the LCU enclosure to gain access to the radio.
One such test performed on the LCU is radio receiver sensitivity performance. The sensitivity performance testing is also referred to as Bit Error Rate (BER) testing. The sensitivity performance testing requires a very low amplitude test signal to be applied to the LCU (e.g., LCU receiver), where such low amplitude test signal is typically near the threshold of the LCU receiver""s capability to receive error free messages. However, it has been found through experimental testing in the field that EOT transmissions occurring within a rail yard interfere with the low amplitude test signal. Thus, during the sensitivity performance testing of the LCU, a nearby EOT transmission may interfere with the testing of the LCU thus causing bit rate errors to be recorded. This, in turn, causes an incorrect BER test result.
What is thus needed is a system which is capable of testing an LCU without recording bit errors caused by interfering transmissions. This system would thus be able to accurately test the LCU in an RF hostile environment. The system would also be easy to implement with currently used LCU systems, including stand-alone or integrated LCU systems.
It is therefore an object of the present invention to provide a radio interference detection and screening system for on-locomotive testing of Locomotive Control Unit (LCU) radios.
It is still a further object of the present invention to provide a radio interference detection and screening system which eliminates bit errors caused by interference during testing of the LCU.
According to the invention, there is provided a radio interference detection and screening system and method of use for on-locomotive testing of Locomotive Control Unit (LCU) radios. The system and method of the present invention is adapted for use with a stand-alone LCU or an integrated LCU.
The system of the present invention includes a modulator connected to an RF communications test set. The modulator generates and continuously repeats a short pseudo-random message, arid the RF communications test set receives the message and impresses it onto a signal. A calibrated attenuator and connecting cable are connected between an LCU and the RF communications test set. The attenuator attenuates the message to a preferably low amplitude signal near the threshold of the LCU""s capability to receive error free messages.
An RF interference detection module is connected to the LCU which is capable of detecting interfering transmissions. When the RF interference detection module detects an interfering transmission (e.g., EOT) it will notify the LCU of such detection. The LCU will then take corrective action in order to xe2x80x9ccompensatexe2x80x9d for the interfering transmission. This corrective action includes the suspension of counting of the number of error free messages received from the RF communication test set during the time of the detected interfering signal. Once the RF interference detection module no longer detects the interfering transmissions, the LCU will resume counting the number of error free messages received from the RF communications test set until the completion of the sensitivity performance test. In this manner, bit errors caused by externally transmitted interference are completely eliminated and an accurate BER result may be obtained.
The present invention is also directed to a method of detecting and screening the interfering transmissions. The method of testing the LCU uses low amplitude signals near the threshold of the LCU""s capability to receive error free messages. The method of the present invention further includes counting the low amplitude signals received by the LCU. After each bit of the low amplitude signal is counted, a determination is made as to whether an interfering signal is present. When an interfering signal is present, the method of the present invention provides a signal to the LCU to notify the LCU of such detection. The LCU will then suspend the counting of each received data bit, and will resume the counting of each received data bit when the interfering signal is no longer detected. A pass or fail message will be generated depending on an outcome of the counting and resuming steps.